I also have used the 4 port USB connector, however I never went over 2 flash drives at the same time. I wonder if the constraint is the number of ports or the number of megabytes.
I cannot seem to find out from anyone if a 1 gig usb drive will work. It won't work if the constraint is 512 mg, as indicated by the message after trying to use 3 drives.
Regards,
Jerry